The opera Waldermarsskatten is a fantasy around a real historical event on the island of Gotland on the east coast of Sweden, "The Valdemar Atterdag holding Visby to ransom, 1361". The trade in the Baltic Sea was dominated by the German trading monopoly The Hanseatic League, which existed around 1150-1650. The city of Visby was included in this association. After a plague pandemic in the Nordic countries in the 1350s, the so-called 'black death', in which a third of the population died, the Danish king Valdemar Atterdag wanted the rich merchants of the Hanseatic League to pay for a renewal of their trade privileges. Valdemar set off to Visby with about thirty ships to Gotland at the end of July 1361. Battles were fought, first on the coast-line then at Visby's city wall, and in total around 1 800 Swedes are said to have lost their lives, while the Danes' loss was around 300 souls. An unfair fight, one might think, as the Danish army consisted of German mercenaries, while Gotland was defended by civilian farmers.